Engines are usually designed with the ability to deliver a peak output, although most engine operation is performed well below this peak value. As such, it can be beneficial to operate with some cylinders inducting air without fuel injection as described in U.S. Pat. No. 6,568,177.
Engines are also designed to purge fuel vapors generated in the fuel delivery system through combustion in the cylinders. The approach for such operation described in U.S. Pat. No. 6,568,177 advantageously disables the partial cylinder operating mode when such fuel vapor purging is requested.
However, the inventors herein have recognized that it can be advantageous to deliver fuel vapors to a subset of the engine cylinders, thereby prolonging the ability to operate in a fuel-cut state even when fuel vapor purging is required. However, in such cases, exhaust gasses between cylinders with and without fuel vapor purge can mix. Thus, when attempting to estimate the amount of fuel vapors in the purge flow, the error is diluted since some of the exhaust gasses measured are from cylinders without any fuel vapors.
Therefore, a new method for estimating a fuel vapor quantity from a fuel vapor recovery system for a vehicle having an engine with a first set of cylinders and a second set of cylinders is used. The method comprises operating the first set of cylinders with injected fuel and inducted fuel vapors from the fuel vapor recovery system; operating the second set of cylinders without fuel vapors from the fuel vapor recovery system; mixing exhaust gas from the first and second set; and determining an indication of fuel vapors from a sensor measuring said mixed exhaust gas based on the operation of the second set of cylinders.
In this way, it is possible to take into account the cylinders without fuel vapors.